An adaptive delta modulator for producing a delta coded output signal in response to an input signal, comprising a filter whose input signal in a pulse sequence derived from said delta coded output signal by a logic processing circuit and whose output voltage determines the instantaneous quantizing unit of said delta modulator.
Such a delta modulator is well known and disclosed in, for example, German patent application No. 28 49 001. Owing to the unavoidable tolerance when implemented with semiconductor components--this delta modulator does not produce a periodic 0-1 sequence at its output when the input signal to be coded assumes zero value. This causes an increase of the idle channel noise in the decoded signal at the receiving end and an aggravation of the clock recovery.